Optical transceiver modules or packages employed in telecommunications, fiber optic and server applications typically contain active electronic devices such as semiconductor lasers that must be hermetically sealed within the package to protect them from variations in humidity, dust and other ambient conditions.
Traditionally, glass frit seals and seam welds have been used to create hermetic seals in ceramic packages. Recently, much attention has been directed to replacing ceramic packages with Transistor Outline Metal-Can packages (or “TO can packages”). In a TO can package, hermetic sealing is achieved by projection welding. TO can packages capable of operating in excess of 10 Gbps are quite expensive, however. In contrast, micro-mechanical system (MEMS) packages made using batch processing techniques are capable of providing data rates in excess of 40 Gbps at much lower cost. Like TO can packages, ceramic packages are relatively expensive, and certainly more expensive than most MEMS packages formed of semiconductor material.
In a MEMS package, active components such as lasers and detectors are preferably mounted on a silicon submount. Passive components such as resistors and capacitors may be integrated onto the submount, or surface mounted on the submount. After assembly of such components on or in the submount has been completed, a lid is placed atop the submount and hermetically sealed thereto. Hermetic sealing of the lid to the submount must occur, however, under ambient conditions that will not damage or destroy the active and passive components mounted on or in the submount.
High frequency electrical signals must also be routed between the inside and outside of the package, and therefore the submount is usually not flat. Consequently, the sealing material employed to form the hermetic seal between the submount and the lid must have a relatively low viscosity to accommodate seal height variations. Finally, a high degree of precision is required to align the lid with the submount before and during sealing.
Frit glass and solder are materials often used to provide the aforementioned hermetic seals. Organic materials such as epoxy may also be employed to provide “near-hermetic” seals. In most cases, the sealing material is deposited onto the submount or the package before sealing occurs. A soldering preform material may also be inserted between the submount and package.
In general, a minimum thickness of sealing material is required to form a joint of sufficient reliability between the lid and submount. A joint that is too thin may have insufficient reliability and strength. A joint that is too thick may result in excessive squeeze-out of sealing material, more about which we say below.
A conventional process for hermetically sealing a lid to a submount involves pressing the lid onto the submount while the sealing material disposed therebetween is in a flowable state. When using frit glass or solder as the sealing material, the ambient temperature is raised until the glass or solder becomes at least partially flowable or malleable, at which point the lid and submount may be joined together.
While pressing or placing the lid atop the submount and onto the malleable or flowable sealing material, some sealing material may be expected to squeeze out of the joint area. The location and shape of the material squeezed out of the joint is very difficult, if not virtually impossible, to control. This problem is especially acute when solder is employed as the sealing material, and often results in random rogue balls of solder forming inside or outside the package. Squeezed-out sealing material such as balls of solder may cause problems in a package, by reducing joint reliability, reducing joint strength, shorting out or damaging circuits or components inside the package, and/or diminishing RF performance if the squeezed-out material is near an RF component.
What is needed is a method and corresponding device for controlling the squeeze-out of sealing material in hermetically sealed electronic modules or packages.
Various patents containing subject matter relating directly or indirectly to the field of the present invention include, but are not limited to, the following:
U.S. Pat. No. 6,194,789 to Zhou for “Flexible hermetic sealing,” Feb. 27, 2000.
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U.S. Patent Publication No. 20030197254 to Huang for “Package for enclosing a laser diode module,”Oct. 23, 2003.
U.S. Patent Publication No. 20030223709 to Lake at al. for “Methods of sealing electronic, optical and electro-optical packages and related package and substrate designs,” Dec. 4, 2003.
U.S. Patent Publication No. 20040086011 to Bhandarkar for “Planar and wafer level packaging of semiconductor lasers and photo detectors for transmitter optical sub-assemblies,” May 6, 2004.
The dates of the foregoing publications may correspond to any one of priority dates, filing dates, publication dates and issue dates. Listing of the above patents and patent applications in this background section is not, and shall not be construed as, an admission by the applicants or their counsel that one or more publications from the above list constitutes prior art in respect of the applicant's various inventions. All printed publications and patents referenced herein are hereby incorporated by referenced herein, each in its respective entirety.
Upon having read and understood the Summary, Detailed Descriptions and Claims set forth below, those skilled in the art will appreciate that at least some of the systems, devices, components and methods disclosed in the printed publications listed herein may be modified advantageously in accordance with the teachings of the various embodiments of the present invention.